According to the following video by EverythingApplePro, 70 changes and tweaks can be seen below:

Overall, iOS 12 beta 2 no longer has apps crashing as frequently, has speed improvements and also lag has been reduced, while GPS now functions properly again.

Some minor tweaks include Notification Centre which now has a larger and brighter ‘x’ icon, while the App Store gains a new personalization tab. You can now 3D Touch on ‘Now Playing’ in Music, while some icons in the Share sheet have been redesigned.

The battery settings interface also gains some tweaks, while a new Siri suggestions tab allows users to toggle on and off apps. Users can now setup screen time for family members, while new splash screens are available to describe new system features.

The second beta of iOS 12 takes less space than the first beta and Geekbench results remain relatively the same.